1. Field of the Invention
The present invention relates generally to a temperature control circuit, and more particularly to a proportional temperature controller for a PTC heater in a laminator.
2. Description of the Related Art
U.S. Pat. No. 4,745,430 discloses a malfunction detecting device in a temperature control circuit for an image fixing station of a photocopier. A heater mounted within a roller in the fixing station is connected to an AC power supply by a triac. Triggering of the triac is controlled by a circuit having two resistance bridges connected to the inputs of a comparator, one resistance bridge having a thermistor as a temperature sensing element. The output of the comparator drives a transistor that causes the trigger circuit to output a high signal at the triac gate. A combination of a ready circuit and an AND gate transmit a signal to a microcomputer for prohibiting copying when the heater temperature falls below 150.degree. C.
U.S. Pat. No. 3,947,656 discloses a temperature controlled cartridge heater for severing vinyl film. A tubular sheath contains heating elements controlled by a comparator-detector using an RCA 3079 integrated circuit triggering a triac. A thermistor in one leg of a bridge circuit with a resistor in the other leg is input to the integrated circuit, which triggers the triac to connect or disconnect power to the heating elements.
U.S. Pat. No. 3,705,289 discloses a controlled heater in an electrostatic copier, in which a temperature varying resistor in one branch of a bridge circuit is fed to a differential amplifier that switches a relay to apply energy to a heating coil. A lamp and motor are controlled through two threshold circuits.
U.S. Pat. No. 4,599,128 discloses an apparatus and process for producing metal clad laminates for circuit boards. The layers are fed through a dual belt press having two pairs of rotating drums supporting the two belts and between which is a pair of heated pressure plates.
U.S. Pat. No. 4,416,719 discloses an identification card laminating apparatus having a pair of rollers heated by heating lamps.
U.S. Pat. No. 5,081,340 discloses a heating element for a plastic film laminator having an aluminum base with conductive silicone in grooves formed in the base. Two such elements are mounted to form upper and lower heating elements.